If it's what I think it is, I've used that media in one of my reactors before and it did pretty well for phosphate removal. Not nearly the pulverization (I think I made that word up) concern as with the phosban, so flow from a mag 5 in a sock shouldn't break it up. Given your specific circumstance as a curing tank with no livestock, not a bad idea. Give it a shot and keep an eye on the pellets to make sure they aren't getting destroyed. If they are, maybe you could put it in a media bag inside the sock...
Regardless, check your param's before you put it in, and continue to check. The phosphate values should drop quickly (1-2 days). Take the media out if the value stops dropping or reaches 0 to keep the phosphate from leaching back out of the media into the water.